Control apparatus



'April 18, l944 l.. o. GRoN'DAHL Erm.

CON TROL APPARATUS Filed Oct. 8, 1941 1w .1%. M NM@ M S w..- y.

K .8 f NN man w .W H MPM m 0. [Nom 47. NN .SNBWM//m S N .Lmwfu Patented Apr. 18, 1944 Lars o. mondani, Pittsburgh, and .raul -NQ Bossart, Cheswick, Pa., assignolfsto The Union Switch & Signal "Company,

Swissvale, Pa., a

corporation of Pennsylvania applicati@ october s, 194.1seria1N`Q- 414,101

12 Claims.

Our invention relatesto control apparatus, and it has particular reference t'o the organization of such apparatus into control systems lfor railroads arranged to provide at the given point a warning or indication that a train is approaching 5 such point. l

It has been proposed heretofore to provide approach control or indications, in cases where the control or indication required is an essential element oi the permanent signal system, by-10 means permanently installed as a portion of the system and usually involving track circuitsjtogether with the neccessary insulated rail joints.

At times, however, it is desirable temporarily to 1 5 approach control o'r indicate the approach of a train at a given point, as for example during the time that a construction .or maintenance crew is working on a given section of track, or for the period that relatively heavy highway traino is caused to travel an unprotected crossing, ordinarily handling va small amount of traic, dueto a detour on a main highway. In these latter cases, the expenseof installing insulated joints,

and the accompanying. interference with traffic 25 moving over the track ,duringl rthe insulation `of the joints, may not warrant the use of the usual track circuit" apparatus for controlling the approach warning or indication devices.

It is an object o`fo`ur present invention te provde systems invdlving readily prtable'and-e'asly installed apparatusarangfe'd tdpiovide' an approacl'i control or indicationfwhen a train approaches a given poirltfn ai-trackway, and which systems are an improvementwupon those shown 3, in a copending application forv Letters Patent of 0 the United States', Serial No. 414,100, l'ed by us on an even date' herewith. l

Another object is to'prcvide means arranged to bel independentl oi the Tusual trackv circuit appa- 4 ratus and functioning'to provide a warning'or indication when atrain approaches a given'point on a trackway. 5

An additional Objectis-'to provide an approach con-trol system involving-readily portable, easily 45 assembled" apparatus larranged to avoid the4 necessity of using line 'wireso cablesextending' along the tracliway. N

A-y further object is to provide-'novel andimproved approach control and indication systems 50 involving track` circuit apparatus arranged to have the range of shunting `effectiveriess," oi Ysuch apparatus lirni't'edby'the frequency-oi the current employed, thusidisp'ensing with-the' necessity for insulated" rail jointsh ordinarilyrequired: t'f" 'con- 5c fine track circuit current to selected portions of irack- The above-rnentioned` 'and other important objects and characteristicieatures which will becomeA readily "apparent, iromtheflollowing description, are attained in-accordanoewith our invention b'y utilizing a source of high frequency oscillations connected across the rails of a stretch, a relay also connectedacross the rails adjacent to` the connection of the source'for energization .from the source, anotherv source, aV circuit control-led by the Arelay vfor connecting one terminal of Athe other source to `a conductor and for connecting the other terminal ofthe'v other source to one rail of the stretch', another relay; a warning` device controlled bythe other relay, and means connected across the conductor and the one track rail, at a point vremote from Vthe first relay, for energizing theother 5 relay from the 0 other source.

VVl/'eshall describe several forms of apparatus embodying our invention, and shall then point out the'novel features thereof inclaims.

`In the accompanying lldravwing, Fig. 1 is a diagrammaticv views'ho'wing one form ofapparatus embodying our invention. Fig. 2'fis--a'diagrammatic view illustrating a modiediorm'of the apparatus represented in Fig. 1, and also embodying our invention.- Fig.y 3 is a diagrammatic View 0 illustrating a modicationjof afportio'n 'oi the Aapparatus represented in Fig. 2,' and also embodyring our invention;` In each 'of the se`,v 'eralviews,

similar reference characters have been employed to designate corresponding parts. l A' Referring to Fig; 1, thereferencecharacter X designates va stretch of railwaytrack over which traflic normally moves in the direction indicated by an arrow or from left tov-right as'view'ed in the drawing. A sourceV of high 'frequency cur- 0 rent, suchas' an oscillator 5, has it's'output terminals connected across' the 'rails I` and Ict of the stretch, and `alf-relay, designated by the reference, character '1"r't,v is'conne'cted, in multiple with the 'rails l and la', to the-output terminalsof oscillator 5 through alrectine t.' The parts' are so proportioned and adjusted that relay TR, normally isfenergized andlpic'keaup', but' aliena-train approaches withinafrlativelylshort distance of, say, 1ll0 feet from theccnnection'of tneos'cillator to the traer tailgate snuntlestabnshd through the wheel'sfani ai'isf-thef tra-ifi lassesthe current in relafyfIR to drop' t'oa value below that reduiredto A lf'i'cild''up relay TR, whereupon that relay releases. After the trai-n passs'beyond the leffective shunting range, relay' 'TRof' course picks up. The frequency of current supplied from oscillator preferably is within the range of, say, 20,000 to 200,000 cycles per second. This high frequency current has a rather high attenuation in the track rails, hence the shunting eiectiveness of a train may be limited to relatively low distances of the order of 100 feet without requiring the use of the usual insulated rail joints normally employed to limit track circuit currents to selected portions of a track.

Relay TR connects a suitable source of current,v

connected across front contact 8 of relay R. Re-

lay lR controls an indicatordevice K over an obyvious circuit including back contact 9 of relay R and a suitable source of current, such as a battery I0.

In the normal condition o f the apparatus, as represented in the drawing, relay R is energized over its stick circuit by current supplied from -battery 1 and transmitted to relay R through the `track circuit comprising rail I and the conductor.

When, however, a train shunt causes relay TR to release, then battery 'I is disconnected from relay R and that relay in turn releases to energize indicator K.y Acknowledging switch AS may now be closed, but relay R of course remains released until the train passes beyond the effective shunting distance of the high frequency track circuit including relay TR. When this happens, relay I TR picks up, and connects battery 'I in circuit with relay R to cause the latter relay in turn to .pick up and open its back contact 9 and close its front contact 8. Indicator K thereupon becomes deenergized, and acknowledging switch AS may be opened to restore4 the apparatus to its normal condition.

From the foregoing, it is apparent that we have provided an approach indication or control sys- `tem controlled by a train shuntable track circuit arranged to have an effective shunting range dened not by the usual rail joints but by the frequency of track circuit current employed. This track circuit apparatus is employedto control an approach relay disposed at a point remote from the track circuit apparatus, and which approach relay is energized over a non-train-shuntable track circuit which involves no line wires or cables extending along the track. The circuit of the approach relay'R isV arranged to have as its two transmission conductors aL track rail and another conductor such as aground-path. It is, of course, to be noted that in the event that our invention is applied to a stretch of multiple track railroad,- a rail of the second track of such road may be employed as the conductor in the place of the ground path represented in Fig. 1.

In Fig. 2,l we have represented the apparatus Aillustrated in Fig. 1 modied for use in connection with a stretch of railroad over which trains oper- `ate in Veither direction, and which apparatus is arranged to provide an indication whenever a train approaches a given point. Referring to Fig. 2, we have represented at D in the drawing, apparatus arranged to cause an indication to be displayed at a remote given point, such as at E, when an eastbound train, operating from left to right as viewed in the drawing, approaches location D. At F we have represented other apparatus arranged to cause an indication to be displayed at E when a westbound train approaches point F.

The apparatus at point D; comprises a first track relay TRI connected through rectifier 6 to the track rails I and I a; an oscillator 5 energized from a suitable source, such as a battery I2, and having its output terminals connected through a circuit including a resistor I3 across the rails I and Ia at a point intermediate E and the connection of relay 'I'RI to the track rails; and two other track relays TR2 and TR3 separately connected across the track rails, each through a rectier 6, at points intermediate E and the connection of oscillator 5 to the track rails. Each relay TR2 andTR3, as indicated in the drawing, is provided with contact arrange- 'ments of the continuity-transfer type arranged in such manner that when deenergized, each relay closes its back contactvprior to opening its front contact, and likewise when each relay becomes energized its front contact is closed before its back contact opens. A suitable 'source of current, such as a generator designated by the reference character f I, has one of its output terminals connected to a conductor, which may comprise a ground path having a ground terminal GI, and has its other terminal normally Aconnected to rail I of the stretch over a circuit which extends from generator fI, through front contacts I4, I5 and I6 of `relays TRI, TR2'and TR3, respectively.

An auxiliary relay, designated by the reference character AR, is provided for at times connecting the other output terminal of the source fl -torail I Aover an alternate circuit path completed at front contact I1 of relay AR. Relay AR is controlled by relays TRI, TR2 and TR3 ,in a manner to be made clear presently.

At the location, E, where it is desired to provide an approach indication, a relay RI is pro- -vided and is coupled to rail I and the conductor by means comprising a transformer. I8 and a resonant rectier unit TUI. Transformer I8 has .its primary winding I9 connected across rail I -and the conductor, and has its vsecondary winding 20 connected through unit TUI to the wind- .ing of relay RI. 'I'he detalls of construction of the resonant rectiiier unit TUI are not shown `in thedrawing since such units are well known in the art, and usually comprise a rectifier and a reactor condenser tuning unitl tuned to resonance at a frequency corresponding to the frequency of current supplied from the source fl. The connection of relay RI to unit TUI preferd 4ably is arranged on the stick circuit principle to include a front contact 2| of relay RI, as can be seen from an inspection of the drawing, and

an acknowledging switch AS is provided for at times completingan alternate path around front .contact 2| of relay RI in the circuit connection Vof theA relay to unit TUI.

Relay RI controls an indicator device K over an obvious circuit including back contact 22 and asourc'eA of current,

`such as a battery 23.

The apparatus at E alscincludes another relay R2 having a function and arranged in a manner to be made clear presently, to be selectively -responsive to current suppliedto rail I and the conductor by apparatus vlocated at point Fand hereinafter described.

,rent supplied from source fl.

.mately one or two seconds.

.denser 3,0 becomes charged.

accanto The apparatus at Dis in its normal condition, as represented in Fig. 2, when the track adjacent to point D is unoccupied by .a train. In this condition of the apparatus, relays .TRL TR2 vand TR3 are energized, and the source fl is connected across. the ground electrode Gi and rail I over the previously traced circuit including a front contact of each of the track relays. Relay-RI at E is picked up, and its ironticontact 2I is closed so `that relay RI is energized by cur- Indicator K accordingly is deenergized.

Relays TRI and TR2 are connected at D to the rails of stretch X, on opposite sides of the connection of oscillator 5 to the rails, at distances fromv the oscillator connection selected to enable a train operating on the track to shunt and cause the iirst encountered one of such re- .lays to be released prior to causingthe release ofthe second relay. If, as hasbeen assumed heretofore, current having a frequency in the range of 20,000 to 200,000 cycles` per second is supplied from oscillator 5, the eiective limits of vsuch current, due to the relatively high attenuation in the track rails, is of the order of 50 to 100 feet, hence the relays TRI and TR2 are preferably spaced apart an appropriate distance of, say, 100 feet. RelayTR3 is employed as a check ing relay, as .will be made clear presently, and relays TR2 and TRB, although separately connected to the rails, are connected to the rails relatively close to each other so that both relays will be substantially simultaneously shunted and released by a train on the stretch.

When an eastbound train approaches D, and comes within the effective shunting range of relay TRI, that relay is shunted and releases to vopen its front contact I4 and thus interrupt the circuit connection of source fI Vto rail l. Relay RI at E accordingly becomes deenergized, and releases to open its front contact ZI and close its Aback contact 22 to energize indicator K. An in- "dication is thus provided at E when an east- V4boundl train arrives at D and shunts relay TRI.

Relays TR2 and TRS are released by the eastbound train-'proceeding toward point E, and when back 4contacts 25 andvZt of relays TR2 and TRS,

respectively, close, relay AR becomes energized 'over a circuit extending from one terminal of rectifier 211 through back contact 25 of relay TRB,

back contact 25 of relay TR2, back contact 28 of relay AR, resistor 29, and the winding of relay AR torthefother terminal of rectifier 21. Rectifier 21 has its. input terminals connected across the terminals of. resistor i3 and hence rectier 2'! is energized from a source of potential obtained from the voltage drop across such resistor. Relay AR has a `condenser connected across its terminals, and .thiscondenser becomes charged in multiple with the winding of relay AR. The circuit of relay AR includes its own back contact 28, hence relay lAR -interrupts its lown energizing circuit at its back 4Contact 2S when the relay picks up. When this happens, condenser 3E) discharges through relay .AR to` maintain the relay in its picked-up position for an appreciable interval, say for approxi- After condenser 30 discharges, relay AR releases and its previously traced circuit is completed at back contact 2B, whereupon relay AR becomes energized, and con- Relay AR again nicks up to open its energizing circuit, condenser 30 again discharges through the relay, and relay "AR again releases to recomplete its energizing cir- "cuit: This `cycle or operation of relay AR is maintainedv untir relays TR2 and vTRS pick up ldue to the passage of an eastbound train and reproximately two seconds, whereas each time the .relay releases, it remains released only a fraction of a second. Each time `that relay AR picks up, its iront contact il closes to complete the previously mentioned alternate circuit, including that contact, over which source fl is connected to rail I.

During the interval relay AR is caused to pick up and release. cyclically, `energy from source JIy is intermittently applied across rail I and thefground return path. This energy, however, may have no useful function at this time since relay RI was caused to release when relay .TRl became shunted, and relay Rl in .releasing opened its front contact 2l to interrupt its stick circuit over which such relay normally is energized. Relay RI accordingly may be picked up only when acknowledging switch AS is closed and energy is impressed from source JI across rail I and the ground.

It is contemplated that the apparatus represented in Fig. 2 will be employed to warn maintenance or construction crews working on the track adjacent to point E that a train is approaching, and it is further contemplated that the warning should he exhibited until the approaching train has passed the work location. Thus, the supervisor or foreman of the track crew would be authorized tol operate acknowledging vswitch AS only after the train has cleared the point at which his crew is working. When this happens, relays TRI, TR2 and TRS of course will be picked up, and the source fl will be constantly connected to rail YI so that when acknowledging switch AS is closed, relay RI becomes energized to deenergize indicator K and to complete its previously traced stick circult.

The above described cyclic operation of relay AR, andY consequent intermittent impression of energy from source fi' across rail I and the ground, has a useful function when a westbound train operates along the stretch. This westbound train will cause, in a manner tov be made clear presently, an indication to be provided at E when the train nears point F. When such train appreaches point D, relays 'FR3 and TR2 are shunted and release simultaneously. When relays TRa` and TR2 release, their back contacts 26 and 2.5 close before their front contacts I5 and It open, hence before source fI is disconnected from rail I at front Contact I5 or It of relay TR2 and TR3, relay AR is caused to become energized, and relay 4AR accordingly picks up to close its front contact Il and complete the alternate circuit connection or source fl to rail l. Relay AR is caused to pick up and release cyclically in the manner described in detail hereinbefore, and relay RI at E is intermittently energized by current supplied to the relay during the intervals that relay AR is picked up. Relay RI has slow releasing characteristics selected to maintain that relay in its energized position during the relatively short intervals that relay AR is released, hence relay Ri is maintained` in its picked-up position to maintain indicator K deenergized. It follows, therefore, that `when a westbound train operates on the stretch,

-shunt from relay TRI.

RI energized and indicator' K accordingly is not pleted when relay TR3 picks up due tothe removal of the train shunt. When relay TR3 picks up, its front contact 33 closes prior to the opening of its back contact 26, and relay AR thereupon becomes energized over a circuit extending from one output terminal of rectifier 21 through front contact 33 of relay TR3, front contact 34 of relay AR, back contact 32 of relay TRI and the winding of relay AR to the other terminal of rectiiier 2'I. This circuit holds relay AR in its picked-up position to maintain source f I connected to rail I during the interval required, after relay TR3 picks up, for the train to remove its When relay TRI picks up, source fl is connected to rail I over its previously traced circuit including a front contact of each of the track relays. Also, relay AR becomes deenergized, and the apparatus at D is restored to its normal condition.

It is to be noted that two separately connected track relays TR2 and TR3 are employed at point D. These relays are arranged to be simultaneously shunted, and both relays are required to release in order to energize relay AR and thus intermittently connect source fl to-rail I over front contact I1 of relay AR. The use of two relays in this manner provides protection against an improper condition in the apparatus which might be caused by an accidental disconnection of a track relay from the track rails. That is to say, should relay TRI become accidentally disconnected from the track rails, the apparatus at D would function to release relay RI at E. A circuit failure or open connection of this relay accordingly would cause the apparatus to fail safe, that is, it causes a Warning indication to be provided, and by a continued display of this warning, furnishes an indication that an improper condition exists and enables the proper steps to be taken to restore the circuit connection of relay TRI. If, however, only one of the two relays TR2 and TR3 is employed to control the auxiliary relay AR, and such track relay becomes disconnected or its circuit connection fails, then` such relay would cause relay AR to be energized, and thus relay RI to be intermittently energized to prevent energization of indicator K when an eastbound train subsequently shunts relay TRI. This dangerous condition is obviated by employing two separately connected track relays to control relay AR, thus requiring a simultaneous failure in the circuits of both relays before a dangerous condition of the apparatus can be established.

It should also be noted that auxiliary relay AR is energized `from a source of potential derived from the voltage drop across resistor I3 interposed in the connection of oscillator 5 to the track rails. 'This arrangement insures that relay AR cannot become energized should the oscillator become disconnected from the track rails, and hence avoid the possibility of maintaining relay RE energized over a front contact of relay AR should the track circuit apparatus be rendered ineffective due to a failure of either the source or its connection to the track rails'.

The apparatus at point F substantially corresponds to the apparatus at point D, with the ex- `-vception that the source of current. connected at F to rail I and the ground terminal GI, has characteristics distinctively different from the characteristics of current supplied at D to the same rail and ground. The source of current at F may, for example, be unidirectional in character, or as shown may comprise a generator f2 of alternating current having a frequency distinctively different from the frequency of currentsupplied from generator JI at D. At E, a resonant rectiiier unit TU 2, tuned to resonance at a frequency corresponding to the frequency of current from generator f2, is connected to secondary winding 20 of transformer I8 and has its output terminals connected to relay R2 over front contact 36 of that relay. Acknowledging switch AS is provided for relay R2, and an indicator KI is energized over back contact 31 of relay R2.

Another difference in the apparatus at F comprises the provision of a condenser 38 and a resistor 39 connected between the heel of contact 28 and one terminal of the Winding of such relay. The capacity of this condenser and the value of resistor 39 are so proportioned that enough energy is stored in the condenser when relay AR is picked up, that when the relay releases, the charge on the condenser, discharging through back contact Z8 and the Winding of relay AR and condenser 3U, causes relay AR again to become picked up and hold up for an interval of the order of, say, four seconds, or for an interval longer than that required for the train to clear relay TRI after having removed its shunt on relaysl TR2 and TR3. This condenser arrangement replaces the stick circuit path previously traced in the apparatus at D for relay AR, and thus obviates the possibility of a dangerous condition existing in the apparatus should relay 'IRI fail to pick up due to an open circuit connection in its circuit. Thus, for example, should relay TRI at D fail to pick up after a westbound train clears the location, the relay would remain down and relay AR would be maintained energized over its stick circuit, to maintain generator f I connected to rail I. An eastbound train reaching point D would, therefore, not cause an indication to be displayed at E.

The arrangement of the apparatus at F lprecludes this possibility since if relay TRI at F does fail to pick up it cannot maintain relay AR energized and such failure would not cause relay R2 at E to be maintained energized. A failure would be detected, however, due to the fact that when relay AR does release after the discharge of condenser 30, the normal circuit over which generator f2 is connected to rail I cannot be completed at front contact I4 of relay TRI, and the continued energization of indicator KI when no train occupies the stretch provides a means of indicating that the apparatus at F is in an improper condition.

In Fig. 3 we have represented apparatus adapted to be employed at point E of Fig. 2, and arranged to modify the system shown in Fig. 2 so as to terminate the energization of the indication displayed at E automatically when the train clears such point. Referring now to Fig. 3, the apparatus represented at E comprises two control relays RI and R2, as represented in Fig. 2, connested across rail I and the conductor through a transformer IBand resonant rectifier units TUI and TU2, respectively. Each relay is connected to its associated resonant rectier unit over its own front contact, and hence such connection involves the stick circuit principle. A single indicator or warning device K is energized whenever either or both relays Rl .and R2 closes its back contact 22 or 31, respectively.

The apparatus .at E 4further comprises an os cillator which has its output terminals connected at E to the rails I and la, and two relays TR4 and TRE connected, in multiple, across the output terminals of oscillator 5, `each through rectifier 6. Relay TR4 is quick acting, while relay TRE is slow acting and has associated therewith a condenser 42 and a resistor 43 arranged to assist in providing such slow acting characteristics. Relays TR4 and TR5 are'normally energized, and are arranged to controla pick-up circuit for control relays Rl and R2.

The apparatus of Fig. 3 functions in the following manner: Assume that an eastbound train operating on stretch X causes the apparatus at D in Fig. 2 to disconnect source fl from its associated track circuit-l Relay RI at E of Fig. 3 accordingly is caused to release, and indicator K becomes energized. As pointed `out hereinbefore, energy is applied to the track circuit of relay R-I when the train passes point D, but since the circuit of relay RI is open at its front contact 2l, relay Rl remains released.

When the train approaches point E of Fig. 3, relays TR4 and TRS become shunted and are caused to release. Relay TRA releases prior to relay TR5, due to the slow acting characteristics of the latter relay, and at this time no useful "i function is served by such relays, except that if desired, an indicator 44 may be provided and energized at this time .over an obvious circuit including front contact 45 of relay TRE, back contact 46 of relay TR4 and the operating element or filament of indicator 44. This indicator may bedesirable to indicate that a train has reached point E.

After the train passes point E and removes its shunt from relays TRA and 'I`R5, relay TRA picks up prior to relay TRS, again due to the slow acting characteristics of the latter relay. When relay TR4 picks up, a pick-up circuit path is then completed, through front contact 41 of relay TR4 and back contact 08 of relay TRS, around front contact 2l of relay RI. Relay RI accordingly becomes energized over its pick-urp circuit during the slow pick-up interval ofy relay TRS, and relay Rlk picks up to close its front contact 2l to complete its stick circuit path, which path holds relay Rl energized after relay TR5 picks up. Relay Ri also opens its back contact 22 todeenergize indicator K. It follows, therefore, that indicator K of Fig. 3 may be energized when an` east.- bound train shunts the apparatus represented at point D in Fig. 2, and may be caused to become deenergized automatically when the eastbound train clears point E. The apparatus at E will, when applied to a highway crossing signal installation, be located adjacent to the highway intersection and indicator K in such event will comprise a highway crossing signal of any suitable form.

After relay TRE picks up at the end of its slow pickup interval, the apparatus at E is restored to its normal ,condition as represented in the drawing.

When relay 'IR is picked up and relay TRE is released, these relays provide a pick-up circuit path for relay R2 around its front contact 36; as is readily apparent from an inspection of the drawing, hence it follows that when a westbound train operates over the stretch and causes'indicator K to be energized in the manner described in detail in connection with .the .apparatus of Fig. 2, relay R2 E is energized and indicator K is caused to become deenergized automatically when the westbound train `clears the apparatus at E.

From the foregoing description of the apparatus represented in Fig. 3, it is apparent -that We have provided means adapted to be incorporated into :the apparatus employed in Fig. 2 and capable .of modifying the apparatus represented in Fig. 2 for use in controlling highway crossing signals. Such a highway crossing signal system is .arranged for use to `provide protection temporarily at crossings where such protection ordinarily is not required but may be required for a short interval not justifying the expense and trouble involved in installing the usual rail joints required for the usual crossing signal systems.

Although we have-herein shown and described only a few forms of control apparatus embodying our invention, itis understood that Various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. In combination, a stretch of railway track comprising electrically continuous track rails, a source of high frequency oscillations of the order of 20,000 cycles per second connected across the rails of said stretch, a relay also connected across said rails adiacent to the connection of said high frequency source for energization from that n, source, another source, a circuit controlled by relay for connecting one terminal of said other source to a conductor and vfor connecting the other terminal of said other source to one rail of said stretch, another relay, a warning device controlled by said other relay, and means connected across said conductor and said one track rail, at a point remote from said first relay, for energizing said other relay from said other source.

2. In combination, a stretch of railway traen `comprising, electrically continuous track rails, a source of high frequency oscillations of the order of 20,000 cycles per second connected across the rails of said stretch, a relay also connected across said rails adjacent to the connection of said high frequency source for energization from that source, another source, a circuit controlled by said relay for connecting one terminal of said other source to a conductor and for connecting the other terminal oi said other source to one rail ci said stretch,` another relay, a warning device controlled by said other relay, and means for coupling said other relay across said conductor and said one rail at a point remote from said first relay.

3. In combination, a stretch of railway track comprising electrically continuous track rails, a source of high frequency oscillations within the range of 20,000 to 200,000 cycles per second connected across the rails of said stretch, a relay also connected across the rails adjacent to the connection ci said source for energization from said source, another relay having one terminal con-- nected to one rail of said stretch at a point remote from said rst relay, a warning device controlled by said other relay, another source, and means controlled by said first relay for connecting one terminal of said other source to the said one rail and having its other terminal connected in circuit to the otherv terminal of the winding of said other relay through circuit means not involving the other rail of said stretch.

4. In combination, a stretch of railway track comprising electrically continuous track rails, two track relays connected across the rails of said track, a source of high frequency oscillations ranging above 20,000 cycles per second so as to have an extremely high attenuation in the track rails connected to said rails at a point intermediate the connection of said relays to said rails, a source of current connected over a front contact'of each of said relays to one rail of said track and to a conductor, another relay coupled at a remote point across said one rail and said conductor, and means controlled by one of said track relays for intermittently connecting said current source across said one rail and said conductor.

5. In combination, a stretch of railway track comprising electrically continuous track rails, two track relays connected at' spaced points across the rails of said track, a source of high frequency oscillations of the order of 20,000

Ycycles per second connected to said rails at a point intermediate the connections of said track relays to said rails, a source of current, another relay at a point remote from said current source, means controlled by front contacts of each of said track relays for energizing said other relay from said current source over a circuit including a front contact of said other relay, means controlled by theone track relay nearer to said other relay for at times maintaining said other relay energized from said current source when the most remote track relay is released, and a warningdevice controlled by said other relay.

.6. In combination, a stretch of railway track having electrically continuous track rails, a source of high frequency oscillations within the range of 20,000 to 200,000 cycles per second connected across said rails adjacent to the connection of said across the rails of said track, two track relays connected across said rails adjacent to the connection of said source for energization therefrom and arranged to be simultaneously shunted by a train in said stretch, one of said relays havin-g slow response characteristics, a control relay controlled from a remote point over a circuit includingr its own front contact, and a pick-up cir-cuit for said control relay including a back contact of said slow pick-up track relay and a front contact of the other of said track relays.

7. In combination, a stretch of railway track having electrically continuous track rails, a source of oscillations in the 20,000 to 200,000 cycles per second band connected across the rails of said track, two track relays connected across said rails adjacent to the connection of said source for energization therefrom and arranged to be simultaneously shunted by a train in said stretch, one of said relays having slow response characteris tics, and an indication device controlled over a circuit including a front contact of said slow response relay and a back contact of the other relay.

8. In combination, a stretch of railway track having electrically continuous track rails, a high frequency oscillator for generating current within the 20,000 to 200,000 cycles per second band and connected across the rails of said track, two track relays connected across said rails adjacent to the connection of said oscillator for energization therefrom and arranged to be simultaneously shunted by a train in said stretch, one of said relays having slow response characteristics, and

means for governing an indicator device over a circuit including a back contact of said slow response relay and a front contact of the other relay. l 9.v In combination with a stretch of railway track comprising electrically continuous track rails, two track relays connected across the rails of said track at spaced points, a high frequency oscillator for generating a current having a frequency in they 20,000 to 200,000 cycles per second band and connected to said rails at a point intermediate the connection of said track relays to said rails for energizing said track relays, a source of current, a slow releasing control relay associated with said track at a point remote from said source, means controlled by frontcontacts of each of said track relays for energizing said control relay from said source over a rail of said track land a conductor not comprising a rail of said track, a device controlled by said control relay, an auxiliary slow release relay having a condenser connected in multiple with its winding, means for energizing said auxiliary relay overy a circuit including its own back contact and a back contact of the track relay nearer to said control relay, and means controlled by said auxiliary re-l lay when picked up for intermittently connecting said source in circuitwith said control relay for intervals of time separated from each other by other intervals shorter in duration than the re lease interval of said control relay.

10. In combination with a stretch of railway track having electrically continuous track rails, two track relays connected across the rails of said track at spaced points, a high frequency oscillator connectedthrough a resistor to said rails at a point intermediate the connections of said track relays to said rails, said oscillator generating current having a frequency within the range of 20,000 to 200,000 cycles per second and said track relays arranged to be energized by current supplied from said oscillator, a source of current, a slow releasing control relay associated with said track at a point remote from said source, meansv controlled by front contacts of said track relays for energizing said control relay from 'said source over a rail of said track and a conductor not comprising a rail of Isaid track, a' device controlled by said control re'- lay, an auxiliary slow release relay having a condenser.r connected in multiple with its winding, means for energizing said auxiliary relay from a source of potential obtained by the voltage drop across said resistor and over a circuit including its own-back contact and a back contact'of the track relaynearer to said control relay, and means controlled by said auxiliary relay when picked up for intermittently connecting said source in cir- .cuit with said control relay for intervals of time separated yfrom each other by other intervals shorter in duration than the release interval of said control relay.

11. In combination with a stretch of railway track having electrically continuous track relays,

a high frequency oscillator connected acrossthe rails of said stretch for impressing thereon current having a frequency within the range of 20,000 to 200,000 cycles per second, two track relays connected across the rails on opposite sides of the oscillator connections for energization yfrom said oscillator, a slow releasing control relay associated with saidtrack at a point remote from said oscillator, a source of current, means controlled by front contacts of each of said track relays for connecting said source in circuit with said control relay, a device governed by said control relay, an auxiliary slow release relay having an energy storing device connected across its terminals, means for energizing said auxiliary relay over a circuit including its own back contact and 4 a back contact of the one of said two track relays nearer to the control relay, other means for energizing said auxiliary relay over a circuit including its own front contact and a front contact of Said one track relay as well as a back contact of the other of said track relays, and means controlled by said auxiliary relay for maintaining said control relay in its energized position in the event that a train shunts said one track relay prior to shunting the other track relay.

12. In combination with a stretch of railway track having electrically continuously track rails, a high frequency oscillator connected across the rails of said stretch for impressing thereon current having a frequency within the ran-ge of 20,000 to 200,000 cycles per second, two track relays connected across the rails on opposite sides of the oscillator connections for energization from said oscillator, a slow releasing control relay associated with said track at a point remote from said oscillator, a. source of current, means controlled by front contacts of each of said track relays for connecting said source in circuit with said control relay, a device governed by said control relay, an auxiliary slow release relay having an energy storing device connected across its terminals, means for energizing said auxiliary relay over a circuit including its own back .contact and a back contact of the one of said two track relays nearer tothe control relay, a condenser charged in multiplewith the winding of said auxiliary relay and discharging through said auxiliary relay upon release of such relay, and means controlled by said auxiliary rel-ay for maintaining said control relay in its energized position in the event that a train shunts said one track relay prior to shunting the other track relay.

LARS O. GRONDAHL. PAUL N. BOSSART.

CERMFICATE oF CORRECTION. Patent No. 2,5LL6,7LL9. Apr-11 18, 19ML.

LAHS o. GRONDAHL, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correcta'. on as follows Page 6, first column, line lil, claim 6, strike out "across said rails, adjacent to the connecti on of said" g and second column, line h5, claim lO, after "of nser't --eaeh of; line 6h, claim 1l, for "relays" read. --rails; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

signed and sealed this 6th day of June, A. D. 19m.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

